Nine men have been arrested by police investigating suspected racist chanting by football fans.

Police received reports of a group of Charlton Athletic supporters singing racist songs on a train following their FA Cup tie at Fulham on 7 January.

Officers from British Transport police (BTP) and the Metropolitan police, accompanied by Charlton officials, visited homes in Bexley, Greenwich, Lewisham and Bromley, all in south-east London, early on Wednesday and arrested nine men.

Detective Inspector Ashley Cooper, leading the BTP investigation, said the suspects, aged between 20 and 30, were taken to a north London police station and are helping police with their inquiries.

Cooper said: "We launched Operation Midas after a group of men, who we believe to be Charlton supporters, boarded a train at Putney and were heard chanting racist songs – something which was both offensive and extremely intimidating for other passengers on board.

"My team of detectives have worked quickly to gather evidence and, by working closely with Charlton Athletic FC, coupled with excellent CCTV footage, intelligence reports and statements from witnesses, we've been able to move swiftly and make this morning's arrests."

Charlton's chief executive, Stephen Kavanagh, said: "This kind of abhorrent behaviour is totally condemned by our club and, in addition to assisting the police, for our own part we will be seeking to ban for life anyone who is found guilty of racially offensive chanting.

"We have been a pioneer of anti-racism and anti-discrimination initiatives in football, so, although these are isolated incidents and in no way reflect the overwhelming majority of Charlton supporters, these recent arrests are saddening to all those who have worked so hard over many decades."

On Saturday, a 48-year-old man, believed to be a Chelsea fan, was arrested at London's Liverpool Street station on suspicion of racially abusing a woman hours after the club's Premier League match at Norwich City.

The arrest came shortly after a separate incident when a group of Chelsea supporters were allegedly embroiled in racist chanting on a train back from the 0-0 draw at Norwich. No arrests have been made in connection with that incident.